In March of 2005, EPA issued the Clean Air Mercury Rule (CAMR). CAMR requires in part that coal-fired power plants perform continuous mercury measurements. Such measurements can be achieved and/or executed using CMMs that monitor flue gas Hg content. However, CMMs must be routinely tested and/or calibrated by injecting a known amount, sometimes referred to as a spike, of calibration gas into a flue gas system such that the CMM can detect the gas and provide a signal to be analyzed. While CMM calibrations are performed using elemental mercury and the system can be spiked with Hg0, protocol can also require a weekly system integrity check using a National Institute of Standards and Technology (NIST)-traceable source of oxidized mercury.
NIST-traceable sources are currently used because heretofore liquid chemistry conditioning/conversion systems have included sinks such as cold spots that absorb residue(s) or sources such as condensation that desorb residue(s) of gaseous mercury. Such cold spots or sources naturally affect a CMM reading/signal and can produce erroneous results. In addition, dry reduction catalyst conversion systems can be compromised by flue gas-fly ash interactions and site-specific flue gas composition, in particular SO2 concentration. As such, reliable calibration sources for characterizing the measurement system are important for the operation of a CMM.
Currently available technology for delivering oxidized mercury to a CMM for testing includes 1) permeation sources of solid mercuric chloride, 2) liquid sources of HgCl2 combined with an injection system such as the HovaCAL system, and 3) thermal oxidizers such as the Spectra Physics thermal oxidizer. However, heretofore systems have exhibited limitations that have proven difficult to overcome.
For example, calibration gas cylinders for various Hg2+ compounds exist, but can drift in concentration output because of low vapor pressure of the mercury and reactions with stainless steel. As such, use of these types of calibration cylinders with a CMM has proven inaccurate. Regarding permeation sources of solid mercury compounds, such sources have issues similar to the calibrated gas cylinders, with the added difficulty of containing several grams of hazardous material. In addition, permeation sources of HgCl2 are unpredictable, susceptible to breakdown over time, highly temperature-sensitive, and unstable in that elemental mercury can form and be emitted by these devices—all of which can lead to fluctuations in output of elemental and oxidized mercury. As such, using either a calibration gas or permeation source requires a modified EPA measurement to determine the concentration being emitted.
Regarding liquid sources of HgCl2 with an injection system, the HovaCAL system uses a laboratory balance and a carefully metered flow rate to inject a liquid calibration source into the sample stream. The system involves continuous measurement of the mass of a liquid source bottle, which is sensitive to vibrations, and control of the liquid flow rate and temperature. While none of these requirements is impossible to produce in the field, the technique is somewhat complicated and prone to failure. In addition, neither the permeation sources nor the HovaCAL system provide a source of elemental mercury for testing or calibration purposes, which is needed in both cases.
Thermal oxidizers such as the Spectra Physics System use a thermal reactor to thermally react mercury and chlorine in a tube furnace. To monitor the reaction, a simple atomic absorption instrument is built into the device to monitor the concentration of Hg0. When the concentration of Hg0 diminishes to zero, it is assumed that all of the mercury has been converted to a transportable oxidized gaseous form of mercury. However, mercury and chlorine can react to form mercury(I)chloride which, at typical transport tubing/line temperatures, can form a solid and cling to walls or break down and be released as elemental mercury. Another drawback of the thermal reactor method is that the thermal reactor is too large to be placed at a probe tip of a CMM.
Another limitation of current prior art systems is their lack of design to inject oxidized mercury into the probe tip of a CMM and, thereby, minimize spike gas transport distance. Stated differently, prior art systems have not been mountable in a flue gas duct adjacent to the probe of the CMM because of the systems' sensitivity to conditions such as temperature and vibrations and/or its size. Furthermore, some of the prior art systems and methods store and dispense gaseous oxidized mercury into a CMM rather than preparing gaseous oxidized mercury on demand for spiking purposes. Accordingly, there is an ongoing need for catalysts, systems, and processes for producing gaseous oxidized mercury for use in the testing of CMMs.